Who is Gasemu in story of a long way gone?

There is no character named "Gasemu" in the story "A Long Walk to Freedom" by Nelson Mandela. The story focuses on Mandela's own life, and the names mentioned are those of his family, friends, political associates, and fellow prisoners.

It's possible you're thinking of a different book or character.

Could you provide more information about where you came across the name "Gasemu"? That would help me identify the story you're referring to and perhaps provide a better answer.